1. Field of the Invention
The present invention relates to a dispensing device for fluid substances.
More particularly it relates to a dispensing device for fluid substances both in the form of cream and in the form of less viscous products such as sprays, deodorants and the like.
2. Discussion of the Background
In the known art a pushbutton is fixed to a hollow stem projecting from a container. Channels connecting the stem bore to a product dispensing hole are provided in the pushbutton. When dispensing is required, pressurized fluid withdrawn from a container is fed into the stem bore. Downstream of the stem there can be provided either a conventional pump operated by pressing the pushbutton, or a valve which is normally closed but opens on pressing the pushbutton; in this latter case the vessel containing the substance to be dispensed must be under pressure.
This known art has the drawback that on termination of a dispensing operation, all the residual product in the stem and in the pushbutton conduits upstream of the dispensing hole is in contact with air; it can therefore dry out or deteriorate and block the pump or valve and hence prevent correct product dispensing on subsequent use.
To obviate these known problems devices have been conceived such as those described in EP0803294. That document describes a dispensing device comprising a dispensing pushbutton in which a piston is provided from which there projects a stem which when in the non-dispensing position closes the dispensing hole. In this manner the product contained in the stem and in the conduits provided within the pushbutton is isolated from the air, the device hence being not subject to malfunction deriving from incrustations which can form in said conduits.
However the aforesaid device (as in the case of many others present in the known art) presents considerable drawbacks.
It is extremely difficult to mould the pushbutton, usually of plastic, because considerable thickness changes are present in proximity to the joint between the chamber in which the piston slides and the cylindrical portion by which the pushbutton fits onto the stem. These thickness variations generate residual stresses in the moulding, leading to ovalization in that region in which the piston is housed and slides.
This creates considerable problems for the seal between the piston lip and that conduit surface along which the piston slides.